The present invention relates to semiconductor-on-insulator (SOI) structures, and particularly to SOI structures including a thin top semiconductor portion and a thin box laterally surrounded by a dielectric material layer and methods of manufacturing the same.
Advanced semiconductor-on-insulator (SOI) complementary metal-oxide-semiconductor (CMOS) circuits employ a thin top semiconductor layer, or a “semiconductor-on-insulator” (SOI) layer to provide enhanced performance. Further, a thin buried insulator can be employed to enable a backplate formed from an upper portion of a conductive handle substrate underneath the buried insulator layer. The backplate can be employed to bias the devices in the top semiconductor layer.
As the thicknesses of the top semiconductor layer and the buried insulator layer decrease, recesses in shallow trench isolation (STI) structures formed at an edge SOI CMOS devices can result in a leakage current in the SOI CMOS devices. Such a leakage current can result from a contact between a material of a gate structure with an active region of the SOI CMOS devices. Divots, i.e., recessed regions, at the edge of the active region is typically caused by wet etches, such as hydrofluoric acid (HF) etch, that are performed to clean the active silicon regions of the top semiconductor layer before forming gate structures.
In the case of back gate devices that employ a portion of the handle substrate as a backplate, a thin top semiconductor layer and a thin buried insulator layer are employed to maximize the effect of the back gate on SOI CMOS devices. The wet etches can form recesses that extend through the entire thickness of the buried insulator layer, exposing the material of the handle substrate. Deposition of the material for gate electrodes thereafter causes an electrical short between the backplate and the gate electrodes formed above the top semiconductor layer. However, electrical insulation between the backplate and the gate electrodes is necessary for functionality of the back gate devices.